Department

Physical Description

Subjects

DOI

10.15760/etd.6196

Abstract

Throughout its eruptive history, Mount Hood has produced compositionally similar calc-alkaline andesite as lava flows and domes near the summit and basaltic andesitic flows from flank vents. Found within the andesite are slightly more mafic inclusions that are compositionally similar to the host andesite (or host lavas); no inclusions were found in the flank lavas. Host lavas and inclusions have the following mineral assemblage: plag + opx ± cpx ± amp + oxides. Flank lava mineralogy is similar to the inclusions and host lavas, but since they are more mafic they contain olivine instead of amphibole. Average silica content among samples analyzed ranges from 57.6 to 62.7 weight percent; however the incompatible trace element composition is more variable at lower silica contents and becomes less variable at higher silica contents. In terms of incompatible trace element composition, the host lavas and inclusions are either depleted (no amp) or enriched (amp± cpx).

Description

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